Magnetic tape is commonly used to store voice and data information due to its reliability, cost efficiency, and ease of use. Magnetic tape may be made more useful and cost-effective by increasing the density of information stored and decreasing the time required to access this information. Tape may be made wider and data tracks written on the tape narrower to increase the areal density of information stored on the magnetic tape. Tape may be made thinner to increase the volume of information stored on a reel of tape. Tape may be moved past the tape head faster to increase the rate of information transfer. Tape paths may be shortened to decrease access time, decrease costs, and decrease the size and complexity of tape access systems. These factors generally necessitate increased accuracy in positioning magnetic tape relative to tape access components.
Tape is typically wound on one or two reels in a protective housing, such as a cassette or cartridge. The path of magnetic tape leaving its containment housing depends on the positioning of the reel relative to the tape player. Typically, this position is established at the interface of the tape reel and the tape player drive coupling used to spin the tape reel. Current coupling designs locate the reel by mating drive teeth on the coupling with drive teeth on the reel. Fixturing the reel to the coupling using this relatively complex geometry is prone to many types of misalignment errors. These errors, representing the accuracy of tape reel location, can be expressed using a variety of geometric criteria. First, axial difference between the tape centerline of the reel and the tape path centerline of the drive represents a positioning offset in the plane of tape travel. Second, perpendicularity of the tape reel axis relative to the tape path centerline of the drive indicates the angular error of the tape path leaving the reel. Third, run out of the tape reel, typically measured at the outside edge of the reel flange, produces a time-varying error in the tape path. Runout is expressed as two components, the axial variation of the reel flange and the radial variation of the reel flange.
If mating drive teeth on the coupling and reel flange are used to position the tape reel, the drive tooth pattern must be very precisely manufactured. Additionally, if the drive teeth become deformed due to mishandling, wear, debris, or the like, the alignment of the reel could be impacted. Typically, the drive teeth on the reel are made of plastic. These teeth wear, break, and deform differently on different cartridges. Hence, misalignment errors may vary greatly between cartridges.
What is needed is to couple tape drives to tape reels in a manner that does not rely on the geometry of drive teeth. In particular, correct axial positioning is needed to minimize tape path errors. Such a coupling should be implemented within cost and space constraints imposed by commercial tape players and cartridges.